U.S. patent application number 17/570434 was filed with the patent office on 2022-04-28 for apparatus and method for carrying out spatially resolved photoacoustics.
The applicant listed for this patent is TRUMPF GmbH + Co. KG. Invention is credited to Andreas Popp.
Application Number | 20220128457 17/570434 |
Document ID | / |
Family ID | |
Filed Date | 2022-04-28 |
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United States Patent
Application |
20220128457 |
Kind Code |
A1 |
Popp; Andreas |
April 28, 2022 |
APPARATUS AND METHOD FOR CARRYING OUT SPATIALLY RESOLVED
PHOTOACOUSTICS
Abstract
An apparatus for carrying out spatially resolved photoacoustics
includes a sample holder configured to receive a sample to be
examined, an electroacoustic transducer in the region of the sample
holder configured to detect acoustic waves excited by light beams
on the sample, and a light beam device configured to emit a
plurality of light beams that are spatially and temporally
separated from one another onto the sample in order to generate
acoustic waves at spatially separated positions on the sample.
Inventors: |
Popp; Andreas;
(Markgroeningen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TRUMPF GmbH + Co. KG |
Ditzingen |
|
DE |
|
|
Appl. No.: |
17/570434 |
Filed: |
January 7, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/EP2020/069141 |
Jul 7, 2020 |
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17570434 |
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International
Class: |
G01N 21/17 20060101
G01N021/17; G01N 29/24 20060101 G01N029/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 9, 2019 |
DE |
10 2019 210 073.2 |
Claims
1. An apparatus for carrying out spatially resolved photoacoustics,
the apparatus comprising: a sample holder configured to receive a
sample to be examined; an electroacoustic transducer in the region
of the sample holder configured to detect acoustic waves excited by
light beams on the sample; and a light beam device configured to
emit a plurality of light beams that are spatially and temporally
separated from one another onto the sample in order to generate
acoustic waves at spatially separated positions on the sample.
2. The apparatus as claimed in claim 1, wherein the light beam
device comprises: a single light source configured to emit a
primary light beam; a beam splitter configured to split the primary
light beam of the light source into a plurality of secondary light
beams; and a beam deceleration device comprising a beam decelerator
configured to decelerate one of the secondary light beams in
relation to a further one of the secondary light beams in order to
achieve retarded impingement of the secondary light beam in
relation to the further secondary light beam on the sample.
3. The apparatus as claimed in claim 2, wherein the beam
deceleration device comprises a plurality of differently retarding
beam decelerators configured to retard secondary light beams
differently and thus to cause them to impinge on the sample in each
case with a temporal offset with respect to one another.
4. The apparatus as claimed in claim 3, wherein the beam
decelerators are arranged or configured two-dimensionally in
mutually different directions at the beam deceleration device, such
that the secondary light beams impinge on the sample in the region
of a two-dimensional area.
5. The apparatus as claimed in claim 2, wherein a beam decelerator
comprises a high refractive index glass and/or a high refractive
index plastic.
6. The apparatus as claimed in claim 2, wherein a beam decelerator
comprises an optical fiber.
7. The apparatus as claimed in claim 2, wherein the beam
deceleration device comprises a plate with at least one beam
decelerator, the plate being transparent to the secondary light
beams at least in sections.
8. The apparatus as claimed in claim 7, wherein the plate is
configured in an integral fashion.
9. The apparatus as claimed in claim 2, wherein the beam splitter
comprises a diffractive optical element and/or a microlens array
for splitting the primary light beam into the secondary light
beams.
10. The apparatus as claimed in claim 2, wherein the
electroacoustic transducer is integrated into the beam deceleration
device.
11. The apparatus as claimed in claim 1, wherein the apparatus
comprises an oscilloscope configured to process and/or represent
the output signal of the electroacoustic transducer.
12. The apparatus as claimed in claim 2, wherein the beam splitter
is configured in the form of a fiber splitter.
13. A method for carrying out spatially resolved photoacoustics,
the method comprising: splitting a primary light beam into a
plurality of secondary light beams; irradiating a sample with the
secondary light beams, wherein a first secondary light beam is
retarded in relation to a further secondary light beam, such that
the first secondary light beam impinges on the sample after the
further secondary light beam; detecting acoustic waves excited on
the sample by the secondary light beams.
14. The method as claimed in claim 13, wherein a pulsed light beam
is used as the primary light beam.
15. The method as claimed in claim 13, wherein two secondary light
beams are retarded by between 0.01 ns and 10 ns with respect to one
another.
16. The method as claimed in claim 15, wherein all the secondary
light beams are retarded by between 0.01 ns and 50 ns in each case
with respect to another secondary light beam.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of International
Application No. PCT/EP2020/069141 (WO 2021/005068 A1), filed on
Jul. 7, 2020, and claims benefit to German Patent Application No.
DE 10 2019 210 073.2, filed on Jul. 9, 2019. The aforementioned
applications are hereby incorporated by reference herein.
FIELD
[0002] The disclosure relates to an apparatus and a method for
carrying out spatially resolved photoacoustics.
BACKGROUND
[0003] It is known to use photoacoustic spectroscopy or
photoacoustic imaging for examining a sample. These are
non-invasive methods that enable the structural, functional and/or
molecular analysis of a sample.
[0004] The methods are based on the photoacoustic effect, i.e. the
conversion of light into sound waves as a result of the absorption
of electromagnetic waves. In this case, the local absorption of
light leads to the abrupt local heating of the sample and thermal
expansion resulting therefrom. Acoustic waves, particularly in the
ultrasonic range, are generated as a result. The acoustic waves are
measured by means of an electroacoustic transducer. In other words,
a sample to be examined is excited with light and the acoustic
response of the sample is detected by means of a microphone in
order to detect defects of the sample, for example.
[0005] The known apparatuses provide for scanning the sample point
by point in a very time-consuming way. Such apparatuses have been
disclosed by DE 10 2014 012 364 B4, U.S. Pat. No. 6,590,661 B1 and
US 2014/0050489 A1, for example.
SUMMARY
[0006] In an embodiment, the present disclosure provides an
apparatus for carrying out spatially resolved photoacoustics. The
apparatus includes a sample holder configured to receive a sample
to be examined, an electroacoustic transducer in the region of the
sample holder configured to detect acoustic waves excited by light
beams on the sample, and a light beam device configured to emit a
plurality of light beams that are spatially and temporally
separated from one another onto the sample in order to generate
acoustic waves at spatially separated positions on the sample.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Subject matter of the present disclosure will be described
in even greater detail below based on the exemplary figures. All
features described and/or illustrated herein can be used alone or
combined in different combinations. The features and advantages of
various embodiments will become apparent by reading the following
detailed description with reference to the attached drawings, which
illustrate the following:
[0008] FIG. 1 shows a schematic elucidation of the photoacoustic
effect;
[0009] FIG. 2 shows a schematic side view of a first embodiment of
an apparatus for carrying out a photoacoustic measurement using the
photoacoustic effect in accordance with FIG. 1;
[0010] FIG. 3 shows a schematic partial plan view of a further
embodiment of an apparatus for carrying out a photoacoustic
measurement;
[0011] FIG. 4 shows the profile of refractive indices of various
glasses versus the wavelength of light radiating through the
glasses, wherein the glasses are able to be used in the apparatuses
in accordance with FIG. 2 or 3; and
[0012] FIG. 5 shows a schematic plan view of a further embodiment
of an apparatus for carrying out a photoacoustic measurement.
DETAILED DESCRIPTION
[0013] Against this background, the present disclosure provides an
apparatus and a method for carrying out spatially resolved
photoacoustics, the photoacoustics being able to be carried out or
being carried out particularly rapidly, efficiently and thus
cost-effectively.
[0014] The present disclosure provides an apparatus for carrying
out photoacoustic spectroscopy and/or photoacoustic imaging. The
apparatus comprises a sample holder for arranging a sample, a light
beam device for illuminating the sample, and an electroacoustic
transducer, i.e. a "microphone", for detecting acoustic waves
generated on the sample. The light beam device is configured to
emit a plurality of, in particular parallel, spatially and
temporally separated light beams or light pulses onto the sample.
In this case, the light beam device is preferably configured to
space the light beams apart from one another by less than 1 .mu.s,
preferably between 0.1 ns and 10 ns, in particular between 0.4 ns
and 4 ns, particularly preferably between 0.5 ns and 1 ns. As a
result of the practically simultaneous irradiation of a plurality
of points of the sample with a plurality of light beams, the
apparatus is able to rapidly measure a large region of the sample.
In this case, however, as a result of the light beams being
minimally temporally retarded with respect to one another, the
apparatus can still assign the individual detection results of the
electroacoustic transducer in each case to a specific distance
between the sample points and the electroacoustic transducer, i.e.
to a specific location on the sample.
[0015] The sample can be part of the apparatus.
[0016] The light source can be configured in the form of a
laser.
[0017] In a particularly preferred embodiment, the light beam
device comprises a single light source, in particular in the form
of a laser, for emitting a primary light beam and a beam splitter
for splitting the primary light beam into a plurality of secondary
light beams that are spatially separated from one another. The beam
splitter can be configured to split the primary light beam into
more than two, in particular more than 5, preferably more than 10,
secondary light beams.
[0018] The beam splitter can be configured to form secondary light
beams that are spaced apart from one another in two different
directions. The directions can be perpendicular to one another. In
other words, the light beams propagate in mutually parallel
directions of propagation, the light beams being laterally offset
with respect to one another. The beam splitter then forms a
multi-light spot array extending in the area. The beam splitter
makes it possible to carry out, instead of one pointlike
excitation, an excitation with a multiplicity of punctiform
excitations in the area.
[0019] The light beam device can be configured to irradiate the
sample with punctiform secondary light beams. A particularly
precise spatial assignment of the acoustic waves can be effected as
a result.
[0020] With further preference, the light beam device comprises a
beam deceleration device disposed downstream of the beam splitter.
The beam deceleration device comprises at least one beam
decelerator that decelerates a secondary light beam, such that the
secondary light beam that passes through the beam decelerator
reaches the sample later than another secondary light beam that
does not pass through the beam decelerator. The use of a single
light source, the light of which is split into a plurality of light
beams and the latter are retarded differently, allows the
structurally simple and particularly cost-effective configuration
of the apparatus.
[0021] In a further preferred embodiment of the apparatus, the beam
deceleration device comprises a multiplicity of in each case
differently retarding beam decelerators. As a result, a large
sample region can be photoacoustically measured practically
simultaneously with high resolution.
[0022] The beam decelerators need not each be at an individual
distance from the electroacoustic transducer. By way of example,
two beam decelerators can be at the same distance from the
electroacoustic transducer, but can retard the respective secondary
light beams to such different extents that an unambiguous
assignment of the signals initiated by the respective secondary
light beams is nevertheless possible. In order to facilitate the
assignment of the secondary light beams passing through the
respective beam decelerators, however, the beam decelerators are
preferably each at an individual distance from the electroacoustic
transducer.
[0023] The apparatus can comprise a collimator in order to
illuminate the beam splitter uniformly.
[0024] The beam decelerators are particularly preferably arranged
or configured at the beam deceleration device in such a way that
the retardations by the respective beam decelerators increase as
the distance from the center point of the beam deceleration device
increases. This is significant particularly in the case of an
electroacoustic transducer arranged centrally in the region of the
beam deceleration device. This is because otherwise it can happen
that the light beams emitted further from the center point of the
beam deceleration device do arrive on the sample more rapidly than
the light beams in the region of the center point of the sample.
However, the acoustic signal propagation times of the acoustic
waves excited further from the center point to the electroacoustic
transducer are longer, and so it can happen that the two effects
(rapid impingement of the light on the sample but slow propagation
on the sample) compensate for one another, as a result of which the
signals recorded by the electroacoustic transducer cannot be
assigned to a precise location on the sample.
[0025] The apparatus can comprise beam decelerators arranged or
configured offset with respect to one another in the form of a
two-dimensional matrix, that is to say in two different directions
of a plane. As a result, the sample can be irradiated in areal
fashion.
[0026] The beam decelerators can be arranged or configured
equidistantly with respect to their nearest neighboring beam
decelerators, in order to be able to examine the sample
uniformly.
[0027] A beam decelerator can comprise plastic, in particular a
high refractive index plastic. A beam decelerator can comprise a
high refractive index glass in order that the secondary light beam
passing through the beam decelerator is retarded particularly
effectively. Preferably, the majority of the beam decelerators, in
particular all of the beam decelerators, comprise a high refractive
index plastic and/or a high refractive index glass. The refractive
index of the high refractive index glass for light in the visible
range is preferably greater than 1.6, in particular greater than
1.65. By way of example, flint F2, dense flint SF10, lanthanum
dense flint LaSF9 and/or polycarbonate can be used as high
refractive index glass.
[0028] As an alternative or in addition thereto, a beam decelerator
can comprise a fiber that is transparent to the light used, in
particular an optical fiber. Preferably, the majority of the beam
decelerators, in particular all of the beam decelerators, comprise
such a fiber. The fiber can be configured in the form of a
solid-core fiber or a hollow-core fiber. Particularly preferably,
all fibers of the beam decelerators in each case have a different
length.
[0029] At least two, in particular the majority, preferably all, of
the beam decelerators can be formed from the same material. In this
case, the beam decelerators are preferably configured with
different lengths in the radiation-transmission direction. As a
result, the beam deceleration device can be configured in a
particularly simple manner structurally.
[0030] In a further advantageous configuration, because it is
particularly simple structurally, the beam deceleration device
comprises a plate that is transparent to the secondary light beams
used. At least one beam decelerator, in particular a plurality of
beam decelerators, preferably all of the beam decelerators, can be
arranged or--preferably--configured at the plate. The plate can be
configured as fully transparent.
[0031] In this case, the beam deceleration device is particularly
preferably configured in an integral fashion.
[0032] The beam deceleration device can be nailed, clamped together
or adhesively bonded from different optical components, and/or
configured by means of a 3D printer.
[0033] In order to optimize the optical transmissivity of the beam
deceleration device, the beam deceleration device can comprise an
antireflection coating on its side facing and/or facing away from
the beam splitter.
[0034] The beam splitter can comprise a diffractive optical element
(DOE) and/or a microlens array for splitting the primary light beam
into the secondary light beams. The beam splitter can be configured
in the form of a diffractive optical element and/or in the form of
a microlens array.
[0035] In order that the assignment of the acoustic signal arriving
at a specific time can be assigned to a position on the sample in
the simplest possible manner, the electroacoustic transducer is
preferably arranged centrally with respect to the sample, in
particular centrally with respect to the sample holder. The
electroacoustic transducer can be arranged or configured centrally
on or in the beam deceleration device. Particularly preferably, the
electroacoustic transducer is integrated into the beam deceleration
device.
[0036] The electroacoustic transducer can be configured as
described in DE 10 2006 013 345 B4 and/or EP 2 039 215 B1, to the
content of which reference is fully made. The disclosure content of
DE 10 2006 013 345 B4 and of EP 2 039 215 B1 is incorporated in its
entirety in the present description.
[0037] In order to keep the apparatus structurally simple, the
apparatus preferably comprises only a single electroacoustic
transducer for detecting the acoustic waves generated on the
sample.
[0038] The apparatus can comprise an oscilloscope for processing
and/or representing the output signal output by the electroacoustic
transducer. The oscilloscope is preferably configured to attain
more than 1 Gsample/s, in particular more than 10 Gsamples/s,
preferably more than 100 Gsamples/s. As a result, acoustic waves
with a particularly small temporal offset with respect to one
another can still be assessed separately from one another and
assigned to spatial positions of the sample.
[0039] One or more further optical elements, for example focusing
lenses, can be arranged in the beam path of the apparatus.
[0040] In a preferred embodiment, the beam splitter is configured
in the form of a fiber splitter. Particularly preferably, both the
beam splitter and the beam deceleration device are configured in
fiber-optic fashion. As a result, overall from a structural
standpoint the apparatus can be configured particularly simply and
cost-effectively.
[0041] The object is furthermore achieved by means of a method for
photoacoustic imaging and/or photoacoustic spectroscopy, in
particular by means of an apparatus described here, wherein the
method comprises the following method steps: [0042] A) splitting a
primary light beam into a plurality of secondary light beams;
[0043] B) illuminating, in particular in pointlike fashion, a
sample with the secondary light beams, wherein at least one
secondary light beam is decelerated in relation to a further
secondary light beam, such that it impinges on the sample after the
further secondary light beam; [0044] C) detecting acoustic waves
excited on the sample by the secondary light beams using an
electroacoustic transducer.
[0045] One or more further method steps can be carried out before,
after or between the method steps described above.
[0046] In the method, a laser beam can be used as primary light
beam.
[0047] Preferably, a pulsed light beam is used as primary light
beam in the method. The pulse duration is preferably less than 1000
ns, in particular less than 100 ns, particularly preferably less
than 10 ns.
[0048] In one preferred variant of the method, two secondary light
beams, in particular two adjacent secondary light beams, are
retarded by between 0.01 ns and 50 ns with respect to one another.
With further preference, in the method, the majority of the
secondary light beams, in particular all of the secondary light
beams, are in each case retarded by between 0.01 ns and 10 ns with
respect to another secondary light beam.
[0049] Further advantages are evident from the following
description and the drawings. Likewise, the features mentioned
above and those that will be explained still further can be used in
each case individually by themselves or as a plurality in any
desired combinations. The embodiments shown and described should
not be understood as an exhaustive enumeration, but rather are of
exemplary character.
[0050] FIG. 1 shows an apparatus 10 for using photoacoustics when
analyzing a sample 12. In this case, the sample 12 is irradiated
with a light beam 14, in particular in the form of a light pulse,
preferably in the form of a laser pulse. The light beam 14 absorbed
in the sample 12 leads to a thermal expansion 16 and further to an
acoustic wave 18. The latter can generate an electrical signal in
an electroacoustic transducer 20, said electrical signal being
represented in an oscilloscope 22.
[0051] If a relatively large region of the sample 12 is intended to
be examined using the apparatuses known from the prior art, then
the light beam 14 has to be shifted examination point by
examination point (not illustrated in FIG. 1). The examination
becomes very time-consuming and expensive as a result.
[0052] FIG. 2 shows a first embodiment of an apparatus 10. The
apparatus 10 comprises a sample holder 24 for receiving the sample
12. For the purpose of examining the sample 12, the apparatus 10
comprises a light beam device 26. The light beam device 26
comprises a light source 28, here a single light source 28. The
light source 28 can be configured in the form of a laser light
source. Preferably, the light source 28 is configured to emit light
pulses, in particular light pulses having a duration of less than
100 ns, preferably of less than 10 ns. The light source 28
generates a primary light beam 14a, which preferably consists of a
multiplicity of light pulses. The primary light beam 14a can be
shaped by a collimator 30.
[0053] The primary light beam 14a impinges on a beam splitter 32,
which splits the primary light beam 14a into a plurality of, in
particular more than 5, preferably more than 10, particularly
preferably more than 15, secondary light beams 14b. The beam
splitter 32 is preferably configured in the form of a planar
diffractive optical element or in the form of a planar microlens
array. With further preference, the beam splitter 32 is configured
in an integral fashion. The beam splitter 32 is preferably
configured in areal fashion, and emits secondary light beams 14b
spaced apart from one another in two different directions. In other
words, the beam splitter 32 is configured to form a multi-light
spot array, in particular in the form of a multi-laser spot array,
composed of secondary light beams 14b. In order to increase the
effectiveness of the beam splitter 32, the latter can comprise an
antireflection coating 34 on its input side.
[0054] A beam deceleration device 36 is disposed indirectly
or--preferably--directly downstream of the beam splitter 32. The
beam deceleration device 36 can comprise a plate 38. The plate 38
is configured such that it is transparent to the secondary light
beams 14b on its input side at least in the region in which the
secondary light beams 14b impinge. Beam decelerators 40a, 40b, 40c,
40d can be arranged or configured at the plate 38. The beam
decelerators 40a-40d are preferably configured in block-shaped or
rod-shaped fashion. Preferably, all the beam decelerators 40a-40d
have a dedicated length in each case, i.e. mutually different
lengths in each case. The beam decelerators 40a-40d can have the
same cross section, in particular a polygonal, preferably round,
cross section. Only four beam decelerators 40a-40d are illustrated
in FIG. 2 for reasons of clarity. However, the beam deceleration
device 36 can comprise more, in particular more than 10, preferably
more than 20, beam decelerators 40a-40d.
[0055] The beam decelerators 40a-40d can be arranged or configured
in the form of a two-dimensional array. The beam decelerators
40a-40d emit the secondary light beams 14b onto the sample 12 in
each case with individual temporal retardation. This is illustrated
in FIG. 2 by wave packets having propagated to different extents
between the beam decelerators 40a-40d and the surface of the sample
12. In order to increase the effectiveness of the beam deceleration
device 36, the latter can comprise an antireflection coating 42 on
its input side and/or on its output side (not shown).
[0056] In the sample 12, the secondary light beams 14b initiate
local thermal expansions and the latter (as explained with regard
to FIG. 1) initiate acoustic waves, which are registered by the
electroacoustic transducer 20. The oscilloscope 22 represents the
signals of the electroacoustic transducer 20. Since it is known
which secondary light beam 14b is temporally retarded to what
extent, and it is furthermore known which secondary light beam 14b
impinges where on the sample 12, the output signals of the
electroacoustic transducer which are output in a specific order can
be assigned to specific sample positions.
[0057] In the schematic example in FIG. 2, the first output signal
of the electroacoustic transducer 20 would be assigned to the
sample position which was illuminated by the secondary light beam
14b which did not pass through a beam decelerator. The second
output signal would be assigned to the secondary light beam 14b
which passed through the beam decelerator 40a, or to the sample
position assigned by this secondary light beam 14b. The third
output signal correlates with the secondary light beam 14b which
passed through the beam decelerator 40b, etc. Although a large
portion of the sample 12 is illuminated almost simultaneously by a
single light source 28, the output signals of the electroacoustic
transducer 20 can be assigned to specific positions on the sample
12 in a spatially resolved manner.
[0058] FIG. 3 shows a plan view of a part of a further apparatus 10
comprising a beam deceleration device 36. An electroacoustic
transducer 20 is arranged or configured in the middle or centrally
in or on the beam deceleration device 36. Beam decelerators, of
which only beam decelerators 40a-40d are provided with a reference
sign for reasons of clarity, are each at an individual distance
from the electroacoustic transducer 20 in order to enable an
unambiguous assignment of the secondary light beams 14b passing
through the beam decelerators 40a-40d. The beam decelerators
40a-40d are spaced apart from one another in two different
directions R1, R2 in order to attain an areal illumination of a
sample 12 (see FIG. 2) with a plurality of spots.
[0059] FIG. 4 shows a diagram in which the refractive index on the
ordinate is plotted against the light wavelength on the abscissa.
The refractive index of some materials that are preferably able to
be used in beam decelerators 40a-40d (see FIGS. 2 and 3) is plotted
in FIG. 4. In this case, the refractive indices of fluorite crown
FK51A 44a, borosilicate crown BK7 44b, barium crown BaK4 44c, flint
F2 44d, dense flint SF10 44e and lanthanum dense flint LaSF9 44f
are plotted in FIG. 4.
[0060] Different materials or the same material can be used in the
beam decelerators 40a-40d. In the case where the same material is
used in all of the beam decelerators 40a-40d, the beam decelerators
40a-40d have different lengths or optical retardation paths. The
calculation of an optical retardation path is presented below on
the basis of an example:
[0061] Even a light velocity of the secondary light beam in a
vacuum of 299,790,000 m/s and a phase velocity of 187 368 750 m/s
in a beam decelerator comprising a material having a refractive
index of 1.6, results in a velocity difference of 112,421,250 m/s.
In order to achieve a temporal retardation of the secondary light
beams of 1 ns, the optical retardation path (in accordance with
v=s*t) has to have a length of 112 mm. If the oscilloscope is
configured to achieve 160 Gsamples/s, the output signal thus
generated by the electroacoustic transducer can still be sampled
160 times.
[0062] FIG. 5 shows an apparatus 10 comprising a light source 28
configured in particular for generating laser light pulses. The
light source 28 is connected to a beam splitter 32 optically, in
particular via a fiber connection 46. The beam splitter 32 is
configured in fiber-optic fashion, i.e. in the form of a fiber
splitter. A beam deceleration device 36 comprises a plurality of
beam decelerators 40a-40e. The beam decelerators 40a-40e are
configured in each case in the form of an optical fiber. The beam
decelerators 40a-40e are preferably configured identically, apart
from their respective length. The different lengths of the beam
decelerators 40a-40e are illustrated schematically by loops in FIG.
5.
[0063] If a light beam is retarded for example via an additional
fiber path of 1 m, then the laser beam propagates in a fiber in the
form of an optical fiber (refractive index of quartz 1.45) with a
phase velocity of 206,751,724 m/s. This results in a temporal
retardation of 4.85 ns.
[0064] The beam deceleration device comprises an optical head 48.
At the optical head, the light beams coming from the beam
decelerators 40a-40e emerge in the form of free beams and impinge
on a sample 12 or a sample holder 24. The optical head 48,
analogously to the illustration in FIG. 3, can be configured with
two-dimensionally arranged exits for the light beams in order to be
able to scan the sample 12 two-dimensionally.
[0065] Taking all the figures of the drawing jointly into
consideration, the disclosure thus relates in summary to an
apparatus 10 for illuminating a sample 12 with a plurality of light
beams 14, 14b succeeding one another in synchronized fashion.
Acoustic waves 18 generated by these light beams 14, 14b on the
sample 12 are detected by an electroacoustic transducer 20. The
synchronous sequence of the light beams 14, 14b can be achieved by
means of a beam deceleration device 36 comprising at least one beam
decelerator 40a-40e, preferably a plurality of beam decelerators
40a-40e. The beam decelerators 40a-40d can each bring about
individual retardations of the light beams 14b passing through
them, i.e. retardations that are different in relation to the other
beam decelerators 40a-40e. As a result, a large surface area of the
sample 12 can be scanned with rapidly successive light beams 14b
that are assignable to the respective illumination position. The
beam deceleration device 36 can be illuminated by a beam splitter
32. The beam splitter 32 and/or the beam deceleration device 36 can
be configured in a planar fashion. In a preferred embodiment,
proceeding from the light source 28 until the light beams emerge
from an optical head 48 of the beam deceleration device 36, the
apparatus 10 comprises predominantly, in particular completely,
fiber-optic components.
[0066] While subject matter of the present disclosure has been
illustrated and described in detail in the drawings and foregoing
description, such illustration and description are to be considered
illustrative or exemplary and not restrictive. Any statement made
herein characterizing the invention is also to be considered
illustrative or exemplary and not restrictive as the invention is
defined by the claims. It will be understood that changes and
modifications may be made, by those of ordinary skill in the art,
within the scope of the following claims, which may include any
combination of features from different embodiments described
above.
[0067] The terms used in the claims should be construed to have the
broadest reasonable interpretation consistent with the foregoing
description. For example, the use of the article "a" or "the" in
introducing an element should not be interpreted as being exclusive
of a plurality of elements. Likewise, the recitation of "or" should
be interpreted as being inclusive, such that the recitation of "A
or B" is not exclusive of "A and B," unless it is clear from the
context or the foregoing description that only one of A and B is
intended. Further, the recitation of "at least one of A, B and C"
should be interpreted as one or more of a group of elements
consisting of A, B and C, and should not be interpreted as
requiring at least one of each of the listed elements A, B and C,
regardless of whether A, B and C are related as categories or
otherwise. Moreover, the recitation of "A, B and/or C" or "at least
one of A, B or C" should be interpreted as including any singular
entity from the listed elements, e.g., A, any subset from the
listed elements, e.g., A and B, or the entire list of elements A, B
and C.
LIST OF REFERENCE CHARACTERS
[0068] 10 Apparatus [0069] 12 Sample [0070] 14 Light beam [0071]
14a Primary light beam [0072] 14b Secondary light beams [0073] 16
Thermal expansion [0074] 18 Acoustic wave [0075] 20 Electroacoustic
transducer [0076] 22 Oscilloscope [0077] 24 Sample holder [0078] 26
Light beam device [0079] 28 Light source [0080] 30 Collimator
[0081] 32 Beam splitter [0082] 34 Antireflection coating (of the
beam splitter 32) [0083] 36 Beam deceleration device [0084] 38
Plate [0085] 40a-40e Beam decelerator [0086] 42 Antireflection
coating (of the beam deceleration device 36) [0087] 44a Refractive
index of fluorite crown FK51A [0088] 44b Refractive index of
borosilicate crown BK7 [0089] 44c Refractive index of barium crown
BaK4 [0090] 44d Refractive index of flint F2 [0091] 44e Refractive
index of dense flint SF10 [0092] 44f Refractive index of lanthanum
dense flint LaSF9 [0093] 46 Fiber connection [0094] 48 Optical head
[0095] R1, R2 Directions (of the spacings of the beam decelerators
40a-40e)
* * * * *